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I have to tell you that wrought steel does not really exist. There is wrought iron, which is really rare these days.

And weldments cant really cast themselfs.

Any steel form which is substantially mechanically worked (rolled, forged, drawn or otherwise plastically deformed to attain shape and structure) is termed wrought.

What we know as cast iron is iron with very high carbon content. Very low carbon steels are in fact, iron but are termed steel to differentiate from cast iron parts.

Cast iron is highly fluid from the 3%+ carbon which when the casting solidifies, comes out of solution, forming structures which can be brittle (white and gray cast iron). When this carbon is burned out in the basic oxygen furnace, these brittle structures cannot form. Yes, special treatment of cast iron both in the ladle and post-casting can offset these brittle structures. For example, one structure in gray cast iron is graphite flakes which when treated, turn into spheres that resist fracture.

Comment

Keith J, white cast iron is simply grey cast iron cooled more rapidely, because of this rapid cooling the carbon does not separate from the iron. which result in a cementite composite, very hard and brittle. not really weldable in it's original state.
white cast iron is widely used on crusher jaws, balls and liners for ball mills and lathe beds.

It is always a good idea to preheat and post heat any cast piece, as usually they have machined surfaces that has to meet some measuring tolerance, by preheating and postheating a welder highly reduce the chance of warping and residual stress, keeping the part welded as close to the original state.